How do I calculate slope/gradient?
"Rise over run" in the geosciences
Many of us know that the slope of a line is calculated by "rise over run". However, the application of slope calculation can seem a little more complicated. In the geosciences, you may be asked to calculate the slope of a hill or to determine rate by calculating the slope of a line on a graph. This page is designed to help you learn these skills so that you can use them in your geoscience courses.
Why should I calculate slope or gradient?
In the geosciences slope can play an important role in a number of problems. The slope of a hill can help to determine the amount of erosion likely during a rainstorm. The gradient of the water table can help us to understand whether (and how much) contamination might affect a local well or water source.
How do I calculate slope (or gradient) in the geosciences?
Gradient in the case of hillslope and water table is just like calculating the slope of a line on a graph - "rise" over "run". But how do you do that using a contour (or topographic) map?
- First get comfortable with the features of the topographic map of interest. Make sure you know a few things:
- What is the contour interval (sometimes abbreviated CI)?
- What is the scale of the map?
- What is the feature for which you want to know the slope?